OAP: Clinical Anatomy of the Eye (Chapter 6)

fascial sheath

What it is:

Thin, protective membrane/sheath.

Surrounds the eyeball (like a capsule).

Separates eyeball from orbital fat.

Creates a smooth socket for movement.

Attachments:

Posteriorly: Attaches to sclera (1.5mm from corneoscleral junction).

Anteriorly: Fuses with conjunctiva near limbus.

Passageways:

Pierced by ciliary nerves & vessels.

Pierced by vortex veins.

Muscle Sheaths

Tubular sleeves extend from the sheath, investing extraocular muscles.

Levator Palpebrae Superioris

muscle in the upper eyelid responsible for elevating or raising the upper eyelid

Suspensory Ligament (Lockwood’s Ligament)

a crucial structure in the orbit that supports and stabilizes the eyeball within the eye socket

Sclera

the white outer layer of the eyeball

generally not very stretchy and is quite strong.

It's thickest at the back and thinnest where your eye muscles attach

has very little blood supply on its own, so if it gets cut, it heals slowly.

Episclera

thin layer of tissue that lies between the sclera and the conjunctiva

surface layer

has a good blood supply

Episclera

Sclera Stroma

Lamina Fusca

Layers of the Sclera

Episclera

outermost, very thin, rich in blood vessels

Sclera Stroma

main, tough, dense middle layer made of collagen fibers (like strong ropes).

Lamina Fusca

innermost layer, darker because it has pigment cells, and connects to the choroid

visual axis

Line connecting fovea centralis to the cornea's nodal point.

Ciliary Flush

Pronounced vasodilation (redness) due to inflammation involving the episcleral plexus.

Scleral Spur

Triangular projection where ciliary muscle attaches

Lamina Cribrosa

Perforated area of sclera at optic nerve exit (weak point, susceptible to glaucoma damage).

Avascular Structure

Poor blood supply (refers to scleral stroma)

Proprioception

Sense of eye position

Intraocular Pressure (IOP)

Pressure inside the eye

Osteogenesis Imperfecta

Ehlers-Danlos Syndrome

Conditions where sclera can be abnormally thin and blue

Corneoscleral Junction

Where cornea meets sclera

Canal of Schlemm

Circular channel at limbus for fluid drainage

Corneal epithelium
Bowman's layer
Corneal stroma
Descemet's membrane
Corneal endothelium

5 LAYERS OF CORNEA

Corneal Epithelium

Outermost protective layer

protects the eye and is constantly renewing itself

Deepest cells: Columnar cells, attached by hemidesmosomes (anchors)

Superficial cells: Flat, possess microvilli (aid tear film).

Bowman's Membrane

Strong, clear layer below epithelium

It's like a tough, clear film that helps protect the eye and prevent things from getting deeper if the epithelium is scratched

It's acellular, meaning it has no living cells

Consists of randomly arranged collagen fibrils.

Does not regenerate; damage leads to scarring.

Corneal Stroma

Thickest layer (approx. 90%).

Made of parallel collagen fibrils (Type I, III, V, VI).

Organized into lamellae (sheets) for transparency.

Contains keratocytes (modified fibroblasts).

made of perfectly organized, layered "sheets" of strong collagen fibers (like clear, perfectly stacked plywood)

Descemet's Membrane

Thin, strong basement membrane.

acts as a basement membrane for the cells on its inner surface.

gets thicker with age

Corneal Endothelium

Innermost layer, pumps fluid out to maintain clarity

Pump function: Actively pumps fluid out of stroma to maintain clarity.

Damage leads to corneal edema (swelling/cloudiness).

Refractive Power

Ability to bend light

The Eyeball

General term for the eye structure

Orbital Cavity

Bony socket housing the eyeball

Anterior Pole

Center of cornea's curvature

Posterior Pole

Center of sclera's curvature

Equator

Imaginary line midway between poles

Myopic Eye (Nearsighted)

Light focuses in front of retina

Hyperopic Eye (Farsighted)

Light focuses behind the retina

Extraocular Muscles

Muscles that move the eyeball

Cornea

clear, dome-shaped covering at the front of each of your eyes

slightly wider than it is tall, and it's thicker at its edges than in the very center.

its curve is very important for proper focusing.

has no blood vessels (it's avascular)

Refractive Surgery (like LASIK)

These procedures change the curvature of the cornea to correct vision problems (like nearsightedness or farsightedness). They essentially reshape this clear "lens."

Transparent

Clear, allows light through

Avascular

No blood vessels (gets nutrients from tears & aqueous humor)

Innervated

Rich nerve supply, highly sensitive

Refraction

Bending of light (cornea is main structure for this)

Astigmatism

Irregular curvature of cornea, causing distorted vision

Corneoscleral Junction (Limbus)

Where cornea meets sclera

Canal of Schlemm

Circular channel at limbus for aqueous humor drainage

“drainpipe”

Scleral Spur

Ridge at limbus where ciliary muscle attaches

Deepest cells (cornea)

Columnar cells, attached by hemidesmosomes (anchors)

Superficial cells

Flat, possess microvilli (aid tear film)

Langerhans' cells

immune cells

Acellular

no cells

Edema of the Cornea

Swelling due to fluid retention (endothelium dysfunction)

Vascularization of the Cornea

Abnormal growth of blood vessels into the normally avascular cornea (can cause opacity).

Regeneration of Corneal Epithelial Cells

Rapid healing of the surface

Corneal Transplants

Grafting a donor cornea (successful due to avascularity and lack of Langerhans' cells in central cornea)

Arcus Senilis

Whitish ring at corneal periphery, common with age

Hassall-Henle Bodies

Small, normal protrusions on Descemet's membrane with age

Aqueous humor

a water-like fluid that lies in front of the lens

Production: By the ciliary body.

Function: Nourishes avascular structures (cornea, lens), maintains intraocular pressure (IOP)

Trabecular Meshwork

the “filter”

Spongy, sieve-like tissue at the iridocorneal angle.

Primary resistance to outflow.

Allows fluid passage via progressively smaller pores.

Aqueous Veins

Connect Canal of Schlemm to deep scleral venous plexus, episcleral venous plexus, and conjunctival veins

Glaucoma

Definition: Disease often characterized by increased intraocular pressure (IOP).

Cause: Blockage/reduced efficiency of trabecular network/Canal of Schlemm. Tissue debris, inflammatory exudate can cause blockage. Thickening of trabecular meshwork with age.

Consequence: Increased IOP leads to atrophy (damage) of the optic nerve and visual field defects.

Most Common Cause of Blindness: Emphasizes its severity.

Anterior Chamber

Space between cornea and iris/pupil

Iridocorneal Angle (Anterior Chamber Angle)

Angle formed by the iris, cornea, and ciliary body, where the trabecular meshwork is located

Anatomic Limbus

Defined by merging of cornea & sclera

Surgical Limbus

Transition zone between bluish cornea and opaque white sclera; important for surgical entry

External Scleral Sulcus

Shallow groove on outer surface of limbus

Internal Scleral Sulcus

Contains trabecular meshwork and Canal of Schlemm

Line of Schwalbe

Line on inner corneal surface, anterior border of trabecular meshwork

Transcellular Channels

Formed by endothelial cells (vacuoles) of Canal of Schlemm

Choroid

Location: Thin, soft, brown coat lining inner surface of the sclera.

Vascularity: Extremely vascular (rich blood supply).

Pigmentation: Contains melanocytes (pigment cells) making it dark brown.

Function of Pigment: Absorbs excess light, prevents reflection.

Thickness: Thinnest at posterior pole, thickest more anteriorly

Function:

Principal function: supplies the outer retina with nutrients and maintains the temperature and volume of the eye

Conducts blood vessels to other parts of the eye.

May help with heat exchange from the retina.

May assist in regulating intraocular pressure (IOP).

Bruch's Membrane

a very thin, special layer that forms the innermost boundary of the choroid, right next to the retina

Its exact function isn't fully understood, but it helps regulate what passes between the choroid's capillaries and the retina

𓂀 Bruch's membrane
𓂀 Choriocapillaris
𓂀 Sattler's layer
𓂀 Haller's layer

4 Layers of the Choroid

Bruch's membrane

Thin layer of tissue located on the innermost part of the choroid.

Choriocapillaris

Layer made up of capillaries (tiny blood vessels that connect arteries to veins).

Intermediate layer

Sattler's layer

Layer of medium blood vessels

Haller's layer

Outermost layer of the choroid that contains large blood vessels

Arterial Supply

Primarily from posterior ciliary arteries (branches of ophthalmic artery), also anterior ciliary arteries

Venous Drainage

Four or five vorticose veins (pierce sclera to drain into ophthalmic veins)

Nerve Supply

Innervated by long and short ciliary nerves (branches of nasociliary nerve, trigeminal nerve).

Carry sensory, sympathetic, and parasympathetic fibers.

Sympathetic stimulation causes vasoconstriction (narrowing) of choroidal blood vessels.

Ciliary Body

ring-shaped structure in the eye located behind the iris

produces the fluid in the eye called aqueous humor

Location: Continuous ring, posterior to iris, anterior to choroid.

Main Functions:

1. Production of Aqueous Humor.

2. Involved in Accommodation (changing lens shape for focus).

Pars Plicata

Pars Plana

Parts of the Ciliary Body

Pars Plicata

Anterior, ridged/plicate portion with ciliary processes

Pars Plana

Posterior, flatter, smoother portion

accommodation

refers to the eye's ability to automatically focus on objects at varying distances, primarily through the ciliary muscle's adjustment of the lens's shape

Ciliary Muscle

This is a ring of smooth muscle within the ciliary body.

It has different types of fibers (longitudinal, radial, circular) that all work together.

When these muscles contract, they reduce the tension on the "suspensory ligaments" that hold the lens

Function: Contraction of ciliary muscle relieves tension on suspensory ligament, allowing lens to round up (for near vision/accommodation).

Innervation: Postganglionic parasympathetic fibers from oculomotor nerve

Suspensory Ligaments (Zonule Fibers)

Think of these as tiny threads or wires that connect the ciliary body to the lens.

When the ciliary muscle contracts, these threads loosen, allowing the lens to become rounder and thicker, which helps you focus on near objects.

When the muscle relaxes, the threads pull taut, making the lens flatter for distant vision.

Ciliary Epithelium

This is a double layer of cells covering the ciliary body.

The inner layer is responsible for producing the aqueous humor

Longitudinal/Meridional fibers

Most external, attached to scleral spur, pull ciliary body posteriorly.

Oblique/Radial fibers

Run from first layer to third layer

Circular fibers

Most internal, run around eyeball like a sphincter

Finger-like projections from the pars plicata.

Covered by ciliary epithelium.

Site of aqueous humor production

Ciliary Processes

Ciliary Epithelium

Two layers of cuboidal cells covering the ciliary processes

Inner nonpigmented epithelium

Responsible for active transport of ions and water, leading to aqueous humor production.

Outer pigmented epithelium

Contains melanin, continuous with retinal pigment epithelium

Ciliary Stroma

Loose connective tissue within the ciliary body.

Contains blood vessels, melanocytes, embedded ciliary muscle

Ora Serrata

Scalloped edge marking the anterior boundary of the neural retina, where it meets the pars plana.

Iris

the area of the eye that contains the pigment which gives the eye its color

This area surrounds the pupil, and uses the dilator pupillae muscles to widen or close the pupil

comes from special pigment cells called melanocytes

Function: allows the eye to take in more or less light depending on how bright it is around you.

Definition: Thin, contractile (can change shape), pigmented diaphragm.

Central Aperture: The pupil.

Location: Suspended in aqueous humor, between cornea and lens

Thickness: Thickest near pupillary margin, thinnest at ciliary margin.

Color: Determined by amount of melanin in melanocytes within the stroma.

Peripheral Margin

Where iris attaches to the ciliary body

Pupillary Margin

Edge surrounding the pupil

Sphincter Pupillae Muscle

Dilator Pupillae Muscle

2 sets of tiny muscles that control the pupil's size (iris)

Sphincter Pupillae Muscle

This muscle forms a ring around the pupil. When it contracts, it makes the pupil smaller (like closing a drawstring bag)

Dilator Pupillae Muscle

These muscles radiate outwards from the pupil. When they contract, they pull the pupil open, making it larger